In a display panel such as an organic EL display panel, a plurality of pixels arranged in a matrix constitute a display area. Each of the pixels is composed of subpixels corresponding to three colors red, green, and blue. The subpixels each include a light emitting layer of the corresponding color. The light emitting layers in the subpixels are separated from each other by a partition wall called “bank”. The light emitting layers are each formed in a different one of openings of the partition wall, according to color. Examples of the partition wall include: a line bank for separating the plurality of subpixels on a column basis; and a pixel bank for separating the plurality of subpixels on a subpixel basis.
The partition wall is typically formed using a photosensitive resin. For example, a positive photosensitive resin or a negative photosensitive resin is applied onto a substrate, and exposed and developed using a photomask (reticle) having a predetermined mask pattern, thus forming the openings. The partition wall of the predetermined shape can be formed in this way.
Larger substrates are used in larger screens of display panels in recent years. This makes it difficult to form the partition wall of the predetermined shape in one operation using one photomask. In view of this, a method (division exposure) of dividing the area for forming the partition wall into a plurality of areas and exposing the plurality of areas using a plurality of photomasks corresponding to the plurality of areas has been proposed. Even in the case where the substrate is not large, division exposure may be needed depending on the type of exposure device.
A partition wall formation method by division exposure is described below, with reference to FIG. 16. FIG. 16 is a diagram for describing a conventional partition wall formation method by division exposure. (a) in FIG. 16 is a plan view of a typical display panel, and (b) in FIG. 16 is a partially enlarged view of a display area in the display panel.
As shown in (a) in FIG. 16, a plurality of pixels 1300 arranged in a matrix constitute a display area 1200 of a display panel 1100. When forming the partition wall in the display area 1200 of the display panel 1100, for example, the display area 1200 is evenly divided into nine areas (blocks) as shown in (a) in FIG. 16. In detail, one photomask corresponding to each of nine division areas 1200A to 1200I is prepared, and exposure is performed nine times for the nine division areas 1200A to 1200I in sequence using the photomask, to expose the whole display area 1200. After the whole display area 1200 is exposed, development and the like are performed to form the openings. The partition wall of the predetermined shape can be obtained as a result.
However, simply dividing the display area in the above-mentioned manner causes the following problem. The photomask is positionally deviated for each division area due to an exposure accuracy problem, which makes the photomask joint (division line) in the partition wall noticeable. In detail, in the case where the photomask is not accurately aligned for each of the nine division areas 1200A to 1200I in (a) in FIG. 16, the pattern of the partition wall is misaligned between adjacent pixels at the photomask joint. As an example, the pattern of the partition wall in a pixel 1300D corresponding to the division area 1200D and the pattern of the partition wall in a pixel 1300E corresponding to the division area 1200E which is right-adjacent to the division area 1200D are misaligned in the pixel column direction as shown in (b) in FIG. 16.
In view of this, the following patterning method has been proposed (see Patent Literature (PTL) 1). In the case of performing division exposure, one photomask overlaps another photomask at the photomask joint. The mask pattern in the photomask overlapping part is, for example, a pixelwise zigzag pattern so that the division line is not linear.
The patterning method disclosed in PTL 1 relates to patterning of pixel electrodes and the like. As shown in FIG. 17, a first photomask 2100 and a second photomask 2200 each have an overlapping part corresponding to pixel patterns of three pixels. Patterning areas 2101 and 2201 of the respective first photomask 2100 and second photomask 2200 and light shielding areas 2102 and 2202 of the respective first photomask 2100 and second photomask 2200 are alternately arranged in a zigzag in the vertical and horizontal directions. Hence, even when misalignment occurs at the photomask joint, such misalignment can be made less noticeable.